DYNAMIC ANALYSIS OF CMUTs IN DIFFERENT REGIMES OF OPERATION

Transcription

1 DYNAMIC ANALYSIS OF CMUTs IN DIFFERENT REGIMES OF OPERATION Baris Bayram, Edward Hæggström, A. Sanli Ergun, Goksen G. Yaralioglu, and Butrus T. Khuri-Yakub Ginzton Laboratory, Stanford University, CA 2003 IEEE Ultrasonics Symposium, Honolulu, Hawaii This work is funded by Office of Naval Research

2 Outline Motivation FEM model of a single CMUT cell Dynamic FEM analysis Results Conclusion

3 Motivation Goal: Low voltage, high frequency CMUTs with more output power & less nonlinearity Method: Investigate different operation regimes for CMUTs: Conventional (no contact) (always in contact) Collapse-snapback (intermittent contact)

4 Different Operation Regimes

5 FEM model of a single CMUT cell Axisymmetric 2-D model Electrical Properties Structural Properties Fluid-structure Interface Acoustic Wave Equation Exact Absorbing Boundary (Grote et al) Basic Properties Collapse: 80 V Snapback: 50 V Resonance: 5 MHz

6 Dynamic FEM Analysis Commercially available software (ANSYS 7.1) Transient Analysis Coupled electrical & structural analysis Fluid medium Contact capability Exact absorbing boundary (Grote et al) Large Signal Characterization Pulse and sinusoidal (AC) excitation Displacement and pressure output Nonlinear distortion: 2 nd harmonic

7 Average Displacement ( m) Pressure (MPa) Results: Pulse Excitation Conventional 0.05 Conventional Time ( s) Time ( s) V BIAS =70V, V PULSE =+5V, t PULSE =20ns Conventional Displacement (p-p) (Å) Resonance freq. (MHz)

8 Results: Pulse Excitation operation V BIAS =65 V Pulse excitation: V PULSE =15V t PULSE =20ns Displacement (p-p): 200 Å, 13 Å/V Pressure (p-p): 2000 kpa, 133 kpa/v

9 Displacement (p-p) (A) Resonance Frequency (MHz) Results: Bias Voltage Conventional Bias Voltage(V) 2 Conventional Bias Voltage(V) V PULSE =+5V, t PULSE =20ns operation: - Higher resonance frequency : contact radius effect - Larger displacement & output pressure

10 Results: AC Excitation operation V BIAS =70 V AC excitation: f EXC =1 MHz V P-P =30V 2 nd harmonic: -23 db Displacement (p-p): 200 Å, 7 Å/V Pressure (p-p): 36 kpa, 1.2 kpa/v

11 2nd order harmonic level (db) Average Displacement (p-p) (A) Results: AC Amplitude Conventional AC Amplitude (p-p) (V) Conventional AC Amplitude (p-p) (V) V BIAS =65 V, f EXC =1 MHz operation: MORE LINEAR RESPONSE

12 Results: Collapse-snapback Collapse-snapback operation V BIAS =70 V AC excitation: f EXC =1 MHz V P-P =40 V 2 nd harmonic: -18 db 3 rd harmonic: -10 db Displacement (p-p): 1200 Å, 30 Å/V Pressure (p-p): 3600 kpa, 90 kpa/v

13 Results: Collapse-snapback Collapse-snapback operation V BIAS =65 V AC excitation: f EXC =5 MHz V P-P =60 V Displacement (p-p): 1600 Å, 26 Å/V Pressure (p-p): 9500 kpa, 158 kpa/v

14 Comparison of Operation Regimes Performance Conventional Collapse- Snapback V BIAS High Low Low V TOTAL <V COLLAPSE >V SNAPBACK >V COLLAPSE <V SNAPBACK Output Power Low Medium High Linearity Good Better Worse

15 Conclusion Investigated different regimes of operation using transient analysis in FEM operation: More linear Low voltage bias Higher frequency Collapse-snapback operation: Higher output pressure Future work: 3D analysis of CMUT arrays